Tunable horn antenna

ABSTRACT

A family of FE dielectric-tuned antennas and a method for frequency tuning a wireless communications antenna are provided. The method comprises: forming a radiator; forming a dielectric with ferroelectric material proximate to the radiator; applying a voltage to the ferroelectric material; in response to applying the voltage, generating a dielectric constant; and, in response to the dielectric constant, communicating electromagnetic fields at a resonant frequency. Some aspects of the method further comprise: varying the applied voltage; and, modifying the resonant frequency in response to changes in the applied voltage. Modifying the resonant frequency includes forming an antenna with a variable operating frequency responsive to the applied voltage. Alternately stated, forming an antenna with a variable operating frequency includes forming an antenna with a predetermined fixed characteristic impedance, independent of the resonant frequency.

RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. ProvisionalApplication 60/283,093, filed Apr. 11, 2001, which is herebyincorporated by reference. In addition, this application relates to thefollowing U.S. applications, which are hereby incorporated by reference:U.S. patent application Ser. No. 09/904,631 filed on Jul. 13, 2001, byStanley S. Toncich entitled “Ferro-Electric Tunable Filter”; U.S patentapplication Ser. No. 09/912,753 filed on Jul. 24, 2001 by Stanley S.Toncich entitled “Tunable Ferro-Electric Multiplexer”; U.S. patentapplication Ser. No. 09/927,732 filed on Aug. 8, 2001, by Stanley S.Toncich entitled “Low Loss Tunable Ferro-Electric Device and Method ofCharacterization”; U.S. patent application Ser. No. 09/927,136 filed onAug. 10, 2001, by Stanley S. Toncich entitled “Tunable MatchingCircuit”; U.S. patent application Ser. No. 10/044,522 filed on Jan. 11,2002, by Stanley S. Toncich entitled “Tunable Planar Capacitor”; U.S.patent application Ser. No. 10/077,654 filed on Feb. 14, 2002, byStanley S. Toncich entitled “Tunable Isolator Matching Circuit”; U.S.patent application Ser. No. 10/076,171 filed on Feb. 12, 2002, byStanley S. Toncich entitled “Antenna Interface Unit”; U.S. patentapplication Ser. No. 10/075,896 filed Feb. 12, 2002, by Stanley S.Toncich entitled “Tunable Antenna Matching Circuit”; U.S. patentapplication Ser. No. 10/075,727 filed Feb. 12, 2002, by Stanley S.Toncich and Tim Forrester entitled “Tunable Low Noise Amplifier”; U.S.patent application Ser. No. 10/075,507 filed on Feb. 12, 2002, byStanley S. Toncich entitled “Tunable Power Amplifier Matching Circuit”.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention generally relates to wireless communicationantennas and, more particularly, to a system and method for tuning anantenna with the aid of a ferroelectric dielectric material.

[0004] 2. Description of the Related Art

[0005] There are several types of conventional antenna designs thatincorporate the use of a dielectric material. Generally speaking, aportion of the field that is generated by the antenna returns to thecounterpoise (ground), from the radiator, through the dielectric. Theantenna is tuned to be resonant at frequencies, and the wavelengths ofthe radiator and dielectrics have an optimal relationship at theresonant frequency. The most common dielectric is air, with a dielectricconstant of 1. The dielectric constants of other materials are definedwith respect to air.

[0006] Ferroelectric materials have a dielectric constant that changesin response to an applied voltage. Because of their variable dielectricconstant, ferroelectric materials are good candidates for making tunablecomponents. Under presently used measurement and characterizationtechniques, however, tunable ferroelectric components have gained thereputation of being consistently and substantially lossy, regardless ofthe processing, doping or other fabrication techniques used to improvetheir loss properties. They have therefore not been widely used.Ferroelectric tunable components operating in RF or microwave regionsare perceived as being particularly lossy. This observation is supportedby experience in Radar applications where, for example, high radiofrequency (RF) or microwave loss is the conventional rule for bulk(thickness greater than about 1.0 mm) FE (ferroelectric) materialsespecially when maximum tuning is desired. In general, most FE materialsare lossy unless steps are taken to improve (reduce) their loss. Suchsteps include, but are not limited to: (1) pre and post depositionannealing or both to compensate for O2 vacancies, (2) use of bufferlayers to reduce surfaces stresses, (3) alloying or buffering with othermaterials and (4) selective doping.

[0007] As demand for limited range tuning of lower power components hasincreased in recent years, the interest in ferroelectric materials hasturned to the use of thin film rather than bulk materials. Theassumption of high ferroelectric loss, however, has carried over intothin film work as well. Conventional broadband measurement techniqueshave bolstered the assumption that tunable ferroelectric components,whether bulk or thin film, have substantial loss. In wirelesscommunications, for example, a Q of greater than 80, and preferablygreater than 180 and, more preferably, greater than 350, is necessary atfrequencies of about 2 GHz. These same assumptions apply to the designof antennas.

[0008] Tunable ferroelectric components, especially those using thinfilms, can be employed in a wide variety of frequency agile circuits.Tunable components are desirable because they can provide smallercomponent size and height, lower insertion loss or better rejection forthe same insertion loss, lower cost and the ability to tune over morethan one frequency band. The ability of a tunable component that cancover multiple bands potentially reduces the number of necessarycomponents, such as switches that would be necessary to select betweendiscrete bands were multiple fixed frequency components used. Theseadvantages are particularly important in wireless handset design, wherethe need for increased functionality and lower cost and size areseemingly contradictory requirements. With code division multiple access(CDMA) handsets, for example, performance of individual components ishighly stressed.

[0009] It is known to use ferroelectric materials for the purpose offrequency tuning antennas. However, the use of FE dielectric materialshas not always been effective, especially if the FE materials are notlocated in the regions of greatest electromagnetic filed densities. Inthe case of a conventional patch antenna, the region of greatestelectromagnetic fields is between the radiator and the counterpoise(ground). As a result of ineffective FE dielectric placement, thechanges in dielectric constant have a minimal effect on changes in theresonant frequency of the antenna. To achieve a useful change inresonant frequency, these conventional FE dielectric antennas have hadto rely on multiple radiators.

[0010] It would be advantageous if the resonant frequency of an antennacould be selectable during use.

[0011] It would be advantageous if FE material could be used to controlthe resonant frequencies of an antenna.

[0012] It would be advantageous if the resonant frequency of an FEmaterial antenna could be changed in response to applying a voltage tothe FE material.

[0013] It would be advantageous if FE material antenna could be used toeffectively change the resonant frequency of a conventional designantenna with a single radiator.

SUMMARY OF THE INVENTION

[0014] The present invention describes antennas fabricated with FEmaterials as a dielectric. The dielectric constant of the FE materialcan be controlled by an applied voltage. Because there is a fixedrelationship between dielectric constant and resonant frequency, theresonant frequency of the antenna can be controlled using the appliedvoltage.

[0015] Accordingly, a method is provided for frequency tuning asingle-band wireless communications antenna. The method comprises:forming a radiator; forming a dielectric with ferroelectric materialproximate to the radiator; applying a voltage to the ferroelectricmaterial; in response to applying the voltage, generating a dielectricconstant; and, in response to the dielectric constant, communicatingelectromagnetic fields at a resonant frequency. Some aspects of themethod further comprise: varying the applied voltage; and, modifying theresonant frequency in response to changes in the applied voltage.

[0016] Modifying the resonant frequency includes forming an antenna witha variable operating frequency responsive to the applied voltage.Alternately stated, forming an antenna with a variable operatingfrequency includes forming an antenna with a predetermined fixedcharacteristic impedance, independent of the resonant frequency.

[0017] In some aspects of the method forming a radiator includes forminga single-radiator.

[0018] In some aspects of the method forming a dielectric withferroelectric material includes: forming the dielectric with adielectric material from a first material having a fixed dielectricconstant; and, forming the dielectric with the ferroelectric materialhaving a variable dielectric constant. Then, modifying the resonantfrequency includes modifying the resonant frequency in response to thevarying the dielectric constant of the ferroelectric material.

[0019] In other aspects, forming a dielectric with ferroelectricmaterial includes forming the dielectric with a plurality of dielectricmaterials, each from a material having a fixed dielectric constant.Alternately or in addition, forming a dielectric with ferroelectricmaterial includes forming the dielectric with a plurality offerroelectric materials, each having a variable dielectric constant.

[0020] Additional details of the above-described method and a family ofantennas fabricated with a FE material dielectric are described below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIGS. 1a through 1 c are views of the present invention patchantenna with a selectable operating frequency.

[0022]FIG. 2 is a cross-sectional drawing illustrating an alternateaspect of the patch antenna of FIG. 1a.

[0023]FIG. 3 is a cross-sectional drawing illustrating an alternateaspect of the patch antenna of FIG. 1a with multiple fixed dielectricconstant layers.

[0024]FIG. 4 is a cross-sectional drawing illustrating an alternateaspect of the patch antenna of FIG. 1a with an internal layer of FEmaterial.

[0025]FIGS. 5a through 9 e illustrate a family of present invention slotantennas.

[0026]FIGS. 10a though 10 d are illustrations of the present inventionopen-ended waveguide antenna.

[0027]FIGS. 11a through 11 e are views of the present invention hornantenna with a selectable operating frequency.

[0028]FIGS. 12a through 12 f are depictions of the present inventionmonopole antenna with a selectable operating frequency.

[0029]FIGS. 13a through 13 f are drawings of the present inventiondipole antenna with a selectable operating frequency.

[0030]FIG. 14 is a flowchart illustrating the present invention methodfor frequency tuning a single-band wireless communications antenna.

[0031]FIG. 15 is a flowchart illustrating an alternate aspect of themethod depicted in FIG. 14.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] The present invention describes a family of antennas with aselectable operating frequency. Generally, each antenna includes aradiator and a dielectric with ferroelectric material proximate to theradiator having a variable dielectric constant. The radiator is resonantat a frequency responsive to the dielectric constant of theferroelectric material. Some antennas include a counterpoise to theradiator. Other antenna designs include a counterpoise and radiator thatare arbitrarily designated. Yet other designs include a counterpoise andradiator that are not distinctly distinguishable from each other.

[0033] In one aspect of the present invention, the family of antennaspresented below have an FE dielectric layer included to effectively tunethe resonant frequency of a single-radiator antenna, unlike prior artantennas which rely upon multiple radiators to achieve any appreciablebandwidth or resonant frequency change. The present inventionsingle-radiator antennas are defined herein as single-band, in that theyeach have one fundament frequency (excluding the consideration ofharmonics of the fundamental) of resonance corresponding to the singleradiator. In another aspect of the present invention family of antennasthe FE dielectric is located in the regions of densest electromagneticfields between the radiator and counterpoise (or virtual counterpoise).As a result, changes in the dielectric constant of the FE materialproduce significant changes in the resonant frequency of the antenna.

[0034]FIGS. 1a through 1 c are views of the present invention patchantenna with a selectable operating frequency. FIG. 1a is a perspectiveview of a single-band patch antenna that may have half-wavelengthradiator dimensions. The patch antenna 100 comprises a counterpoise 102and a dielectric with ferroelectric material 104 overlying thecounterpoise. The dielectric has a varying dielectric constantresponsive to a voltage applied to the ferroelectric material. At leastone radiator 106 overlies the dielectric 104 having a resonant frequencyresponsive to the dielectric constant. In some aspects of the patchantenna 100, the dielectric 104 is a layer consisting entirely of FEmaterial. The principles and design of patch antennas are wellunderstood by those skilled in the art and are not repeated here in theinterest of brevity. Although the use of FE material gives a patchantenna a wider range of selectable operating frequencies, the generalprinciples of design are not changed by the present invention FEmaterial. A coaxial feedline 108 has a center conductor 110 connected tothe radiator 106 and a ground connected to the counterpoise 102.

[0035]FIG. 1b is a plan view of the patch antenna 100 of FIG. 1a.Typically, the dielectric with FE material is only placed in thevicinity of the radiator 106. Area 112 may be a dielectric with a fixedconstant. In alternate embodiments not shown, the FE dielectric 104 maysurround the radiator 106 evenly on all sides, or the dielectric areas104 and 112 may be formed symmetrically around the radiator 106.

[0036]FIG. 1c is a cross-sectional view of an inverted-F planar antenna,such as might be suitable with quarter-wavelength radiator dimensions.The FE dielectric 104 is shown interposed between the single-radiator106 and the counterpoise 102, however, other FE dielectric patterns anddistributions are also practical.

[0037] The antenna 100 has a predetermined fixed characteristicimpedance independent of the resonant frequency. That is, the inputimpedance remains 50 ohms for example, despite the operating frequencyselected. Alternately, it can be said that the antenna 100 has apredetermined approximately constant gain independent of the resonantfrequency.

[0038]FIG. 2 is a cross-sectional drawing illustrating an alternateaspect of the patch antenna of FIG. 1a. As shown, the dielectric 104includes at least one dielectric layer 200 formed from a first materialwith a fixed dielectric constant and a dielectric 202 formed from aferroelectric material with a variable dielectric constant, adjacent thedielectric 200 with the fixed dielectric constant. As shown, thedielectric with the FE material 202 overlies the dielectric with thefixed dielectric constant 200. Typically a voltage is applied to aconductor in the vicinity of the FE dielectric layer 202 to create adesired dielectric constant. The voltage, represented by the “+” and “−”signs can be supplied by voltage generator 203. In some aspects, anelectrical insulator (not shown) can be interposed between layer 202 andthe conductive radiator 106 to isolate the bias voltage from the acsignal voltage. However, a sheet of conductor is usually required toevenly distribute the bias voltage over the FE dielectric 202 thatinterferes with the antenna tuning. Therefore, the dc voltage istypically superimposed upon ac signal being conducted by the radiator,and the reference ground is supplied to the counterpoise 102.Alternately but not shown, the dielectric formed with the fixeddielectric constant 200 overlies the dielectric with the ferroelectricmaterial 202. Again, an insulator might be interposed between the FEdielectric layer 202 and the conductive counterpoise, and a referenceground supplied that is different from the voltage at the counterpoise.However as shown, the FE dielectric layer is typically biased with areference ground supplied to the counterpoise. Note, in some aspects ofthe antenna the bias voltage polarities are reversed from the polarityshown.

[0039]FIG. 3 is a cross-sectional drawing illustrating an alternateaspect of the patch antenna of FIG. 1a with multiple fixed dielectricconstant layers. The dielectric with the fixed dielectric forms a firstlayer 200 a underlying the dielectric with the fixed dielectric constant202, and a second layer 200 b overlies the dielectric with theferroelectric material 202. The two fixed dielectric layers need notnecessarily have the same dielectric constant. Further, the use of threeor more layers of fixed dielectric is also possible. Alternately but notshown, multiple FE layers can be formed around a fixed dielectric layer,or multiple layers of both fixed dielectric and FE layers can be used.The multiple FE dielectric layers may have different thickness, be madeof different FE materials, or otherwise have different dielectricconstants with respect to the same voltage.

[0040]FIG. 4 is a cross-sectional drawing illustrating an alternateaspect of the patch antenna of FIG. 1a with an internal layer of FEmaterial. As shown, the dielectric with the ferroelectric material 202is formed internal to the dielectric 200 with the fixed dielectricconstant. Alternately but not shown, the dielectric with the fixeddielectric constant 200 is formed internal to the FE dielectric 202.Further, multiple internal FE dielectric regions could be used.

[0041] In some aspects, the dielectric with ferroelectric material 202is formed from barium strontium titanate, Ba_(x)Sr_(1−x)TiO₃ (BSTO).However, alternate FE materials are well known and may performequivalently. Returning the FIG. 2 for example, the dielectric withferroelectric material 202 can be formed in a thin film layer having athickness 206 in the range from 0.15 to 2 microns. Alternately, thedielectric with ferroelectric material 202 is formed in a thick filmhaving a thickness 206 in the range from 1.5 to 1000 microns. In someaspects, the dielectric with ferroelectric material has a dielectricconstant in the range between 100 and 5000 at zero volts. In otheraspects, the dielectric formed from the first material with a fixeddielectric constant 200 and the dielectric formed from the ferroelectricmaterial 202 have a composite dielectric constant in the range between 2and 100 at zero volts.

[0042] The dielectric constant of the FE material can be manipulatedthrough doping and control of the Curie temperature (Tc). Some populardopant materials are tungsten (W), manganese (Mn), and magnesium (Mg),introduced as oxides. However, other equivalent elements in the samecolumn of the periodic table may also be practical. An FE material hasits greatest dielectric constant at Tc, with the dielectric falling offrapidly with changes of temperature in either direction. However, thereis typically less change in dielectric constant for temperature aboveTc. Therefore, the Tc of an FE material is typically chosen to be belowthe operating temperature seen by the dielectric material

[0043] An antenna built with a dielectric constant of 1 (air) has lessloss than an antenna built with higher dielectric constant material.However, higher dielectric constant materials are often useful inreducing the size (the effective wavelength) of antennas. Generally, anantenna designer seeks a dielectric material with dielectric constant ofless than 100. The FE material dielectric constants can be reduced byadding dopants at the cost of variability (less change in dielectricconstant per bias volt). Suitable tradeoffs between Tc and doping canmake practical a greater than 2:1 change in FE material dielectric forless than a volt change in bias voltage.

[0044]FIGS. 5a through 9 e illustrate a family of present invention slotantennas. Generally, each single-band slot antenna includes acounterpoise and a dielectric with ferroelectric material overlying thecounterpoise. However, some slots antennas can be understood as justhaving a radiator, or having a virtual radiator and virtualcounterpoise. A slot, formed in either the counterpoise or the radiatorhas an electrical length responsive to the dielectric constant and thedielectric has a varying dielectric constant responsive to a voltageapplied to the ferroelectric material. A radiator overlies and isproximate to the dielectric.

[0045] It is also generally true that the radiator in each of the slotdesigns has a predetermined fixed characteristic impedance independentof the resonant frequency. That is, the electrical length of the slot(s)is constant with respect to the resonant frequency. Alternately, theradiator has a predetermined approximately constant gain independent ofthe resonant frequency. It is also generally true that the slot (orslots) have an electrical length that varies in response to thedielectric constant(s) to be either approximately one-half wavelength ofthe resonant frequency with respect to the dielectric, or approximatelyone-quarter wavelength of the resonant frequency with respect to thedielectric. The principles and design of slot antennas are wellunderstood by those skilled in the art and are not repeated here in theinterest of brevity. Although the use of FE material gives a slotantenna a wider range of selectable operating frequencies, the generalprinciples of design are not changed by the present invention FEmaterial.

[0046]FIG. 5a is a perspective view of the present invention microstripslot antenna 500. A counterpoise 502, a radiator 504, and a dielectricwith ferroelectric material 506 form the microstrip. Typically, thedielectric with ferroelectric material 506 is located in the vicinity ofthe slot, as shown. Away from the slot a different dielectric 507 may beused with a fixed dielectric constant. A slot 508 is formed in thecounterpoise 502. As shown, the slot 508 is transverse to the radiator504, but it need not be. In other aspects of the microstrip slot 500, aplurality of slots (not shown) are used.

[0047]FIG. 5b is a cross-sectional drawing illustrating an alternateaspect of the microstrip slot antenna of FIG. 5a. As shown, thedielectric 506 includes at least one dielectric layer 510 formed from afirst material with a fixed dielectric constant and a dielectric 512formed from a ferroelectric material with a variable dielectricconstant, adjacent the dielectric 510 with the fixed dielectricconstant. As shown, the dielectric with the FE material 512 overlies thedielectric with the fixed dielectric constant 510. Typically a voltageis applied to a conductor in the vicinity of the FE dielectric layer 512to create a desired dielectric constant. The voltage, represented by the“+” and “−” signs can be supplied. In some aspects, an electricalinsulator (not shown) can be interposed between layer 512 and theconductive radiator 504 to isolate the bias voltage from the ac signalvoltage. However, a sheet of conductor is usually required to evenlydistribute the bias voltage over the FE dielectric 512 that interfereswith the antenna tuning. Therefore, the dc voltage is typicallysuperimposed upon ac signal being conducted by the radiator, and thereference ground is supplied to the counterpoise 502. Alternately butnot shown, the dielectric formed with the fixed dielectric constant 510overlies the dielectric with the ferroelectric material 512. Again, aninsulator might be interposed between the FE dielectric layer 512 andthe conductive counterpoise, and a reference ground supplied that isdifferent from the voltage at the counterpoise. However as shown, the FEdielectric layer is typically biased with a reference ground supplied tothe counterpoise. Note, in some aspects of the antenna the bias voltagepolarities are reversed from the polarities shown.

[0048]FIG. 5c is a cross-sectional drawing illustrating an alternateaspect of the microstrip slot antenna of FIG. 6a with multiple fixeddielectric constant layers. The dielectric with the fixed dielectricforms a first layer 510 a underlying the dielectric with the fixeddielectric constant 512, and a second layer 510 b overlies thedielectric with the ferroelectric material 512. The two fixed dielectriclayers need not necessarily have the same dielectric constant orthickness. Further, three or more fixed dielectric layers may be used.Alternately but not shown, multiple FE layers can be formed around afixed dielectric layer, or multiple layers of both fixed dielectric andFE layers can be used. The multiple FE dielectric layers may havedifferent thickness, be made of different FE materials, or otherwisehave different dielectric constants with respect to the same voltage.

[0049]FIG. 5d is a cross-sectional drawing illustrating an alternateaspect of the microstrip slot antenna of FIG. 5a with an internal layerof FE material. As shown, the dielectric with the ferroelectric material512 is formed internal to the dielectric 510 with the fixed dielectricconstant. In some aspects, multiple FE internal regions can be formed.Alternately but not shown, the dielectric with the fixed dielectricconstant 510 is formed internal to the FE dielectric 512. Again,additional electrical insulators might be used to isolate from thecounterpoise 502 and radiator 504 from the FE layer 512.

[0050] In some aspects, the dielectric with ferroelectric material 512is formed from barium strontium titanate, Ba_(x)Sr_(1−x)TiO₃ (BSTO).However, alternate FE materials are well known and may performequivalently. Returning the FIG. 5b for example, the dielectric withferroelectric material 512 can be formed in a thin film layer having athickness 514 in the range from 0.15 to 2 microns. Alternately, thedielectric with ferroelectric material 512 is formed in a thick filmhaving a thickness 514 in the range from 1.5 to 1000 microns. In someaspects, the dielectric with ferroelectric material has a dielectricconstant in the range between 100 and 5000 at zero volts. In otheraspects, the dielectric formed from the first material with a fixeddielectric constant and the dielectric formed from the ferroelectricmaterial have a composite dielectric constant in the range between 2 and100 at zero volts.

[0051] The dielectric constant of the FE material can be manipulatedthrough doping and control of the Curie temperature (Tc). Some populardopant materials are tungsten (W), manganese (Mn), and magnesium (Mg),introduced as oxides. However, other equivalent elements in the samecolumn of the periodic table may also be practical. An FE material hasits greatest dielectric constant at Tc, with the dielectric falling offrapidly with changes of temperature in either direction. However, thereis typically less change in dielectric constant for temperature aboveTc. Therefore, the Tc of an FE material is typically chosen to be belowthe operating temperature seen by the dielectric material.

[0052] An antenna built with a dielectric constant of 1 (air) has lessloss than an antenna built with higher dielectric constant material.However, higher dielectric constant materials are often useful inreducing the size (the effective wavelength) of antennas. Generally, anantenna designer seeks a dielectric material with dielectric constant ofless than 100. The FE material dielectric constants can be reduced byadding dopants at the cost of variability (less change in dielectricconstant per bias volt). Suitable tradeoffs between Tc and doping canmake practical a greater than 2:1 change in FE material dielectric forless than a volt change in bias voltage.

[0053]FIG. 6a is a perspective view of the present invention coaxialslot antenna 600. The counterpoise 602, radiator 604, and dielectricwith FE material 606 form a coaxial line with a slot 608 in thecounterpoise 602. The FE dielectric 606 is proximate to the slot 608.Away from the slot a different dielectric 607 with a fixed dielectricconstant can be used. As shown, the slot 608 is transverse to theradiator 604, but it need not be. In other aspects of the coaxial slotantenna 600, a plurality of slots (not shown) are used.

[0054]FIG. 6b is a cross-sectional drawing illustrating an alternateaspect of the coaxial slot antenna of FIG. 6a. As shown, the dielectric606 includes at least one dielectric layer 610 formed from a firstmaterial with a fixed dielectric constant and a dielectric 612 formedfrom a ferroelectric material with a variable dielectric constant,adjacent the dielectric 610 with the fixed dielectric constant. Asshown, the dielectric with the FE material 612 overlies the dielectricwith the fixed dielectric constant 610. Typically a voltage is appliedto a conductor in the vicinity of the FE dielectric layer 612 to createa desired dielectric constant. The voltage, represented by the “+” and“−” signs can be supplied. In some aspects, an electrical insulator (notshown) can be interposed between layer 612 and the conductive radiator604 to isolate the bias voltage from the ac signal voltage. However, asheet of conductor is usually required to evenly distribute the biasvoltage over the FE dielectric 612 that interferes with the antennatuning. Therefore, the dc voltage is typically superimposed upon acsignal being conducted by the radiator, and the reference ground issupplied to the counterpoise 602. Alternately but not shown, thedielectric formed with the fixed dielectric constant 610 overlies thedielectric with the ferroelectric material 612. Again, an insulatormight be interposed between the FE dielectric layer 612 and theconductive counterpoise, and a reference ground supplied that isdifferent from the voltage at the counterpoise. However as shown, the FEdielectric layer is typically biased with a reference ground supplied tothe counterpoise. Note, in some aspects of the antenna the bias voltagepolarities are reversed from the polarities shown.

[0055]FIG. 6c is a cross-sectional drawing illustrating an alternateaspect of the coaxial slot antenna of FIG. 6a with multiple fixeddielectric constant layers. The dielectric with the fixed dielectricforms a first layer 610 a underlying the dielectric with the fixeddielectric constant 612, and a second layer 610 b overlies thedielectric with the ferroelectric material 612. The two fixed dielectriclayers need not necessarily have the same dielectric constant orthickness. Further, three or more fixed dielectric layers may be used.Alternately but not shown, multiple FE layers can be formed around afixed dielectric layer, or multiple layers of both fixed dielectric andFE layers can be used. The multiple FE dielectric layers may havedifferent thickness, be made of different FE materials, or otherwisehave different dielectric constants with respect to the same voltage.

[0056]FIG. 6d is a cross-sectional drawing illustrating an alternateaspect of the coaxial slot antenna of FIG. 6a with an internal layer ofFE material. As shown, the dielectric with the ferroelectric material612 is formed internal to the dielectric 610 with the fixed dielectricconstant. Note, multiple internal regions can be formed although onlyone is shown. Alternately but not shown, the dielectric with the fixeddielectric constant 610 is formed internal to the FE dielectric 612.Again, additional electrical insulators might be used to isolate fromthe counterpoise 602 and radiator 604 from the FE layer 612.

[0057] In some aspects, the dielectric with ferroelectric material 612is formed from barium strontium titanate, Ba_(x)Sr_(1−x)TiO₃ (BSTO).However, alternate FE materials are well known and may performequivalently. Returning the FIG. 6b for example, the dielectric withferroelectric material 612 can be formed in a thin film layer having athickness 614 in the range from 0.15 to 2 microns. Alternately, thedielectric with ferroelectric material 612 is formed in a thick filmhaving a thickness 614 in the range from 1.5 to 1000 microns. In someaspects, the dielectric with ferroelectric material has a dielectricconstant in the range between 100 and 5000 at zero volts. In otheraspects, the dielectric formed from the first material with a fixeddielectric constant and the dielectric formed from the ferroelectricmaterial have a composite dielectric constant in the range between 2 and100 at zero volts.

[0058] The dielectric constant of the FE material can be manipulatedthrough doping and control of the Curie temperature (Tc). Some populardopant materials are tungsten (W), manganese (Mn), and magnesium (Mg),introduced as oxides. However, other equivalent elements in the samecolumn of the periodic table may also be practical. An FE material hasits greatest dielectric constant at Tc, with the dielectric falling offrapidly with changes of temperature in either direction. However, thereis typically less change in dielectric constant for temperature aboveTc. Therefore, the Tc of an FE material is typically chosen to be belowthe operating temperature seen by the dielectric material.

[0059] An antenna built with a dielectric constant of 1 (air) has lessloss than an antenna built with higher dielectric constant material.However, higher dielectric constant materials are often useful inreducing the size (the effective wavelength) of antennas. Generally, anantenna designer seeks a dielectric material with dielectric constant ofless than 100. The FE material dielectric constants can be reduced byadding dopants at the cost of variability (less change in dielectricconstant per bias volt). Suitable tradeoffs between Tc and doping canmake practical a greater than 2:1 change in FE material dielectric forless than a volt change in bias voltage.

[0060]FIGS. 7a through 7 f are views of the present invention circularwaveguide slot antenna 700. As is well known, in FIG. 7a thecounterpoise and radiator are not distinctly distinguishable, therefore,the circular waveguide antenna is described as comprising a radiator 704and dielectric 706. As shown, the slot 708 is transverse to the radiator704, but it need not be. The FE dielectric 706 is located proximate tothe slot 708. Other, fixed constant dielectric material 707 can be usedaway from the slot 708. In other aspects of the circular waveguide slotantenna 700, a plurality of slots (not shown) are used.

[0061]FIG. 7b is a cross-sectional drawing illustrating an alternateaspect of the circular waveguide slot antenna of FIG. 7a. As shown, thedielectric 706 includes at least one dielectric layer 710 formed from afirst material with a fixed dielectric constant and a dielectric 712formed from a ferroelectric material with a variable dielectricconstant, adjacent the dielectric 710 with the fixed dielectricconstant. As shown, the dielectric with the FE material 712 overlies thedielectric with the fixed dielectric constant 710. Typically a voltageis applied to a conductor in the vicinity of the FE dielectric layer 712to create a desired dielectric constant. The voltage, represented by the“+” and “−” signs can be supplied. In some aspects, an electricalinsulator (not shown) can be interposed between layer 712 and theconductive radiator 704 to isolate the bias voltage from the ac signalvoltage. However, a sheet of conductor is usually required to evenlydistribute the bias voltage over the FE dielectric 712 that interfereswith the antenna tuning. Therefore, slits 709 can be formed in theradiator 704 to separate the two bias voltage polarities. The dcvoltages are typically superimposed upon ac signal being conducted bythe radiator halves. Alternately but not shown, the dielectric formedwith the fixed dielectric constant 710 overlies the dielectric with theferroelectric material 712. Note, in some aspects of the antenna thebias voltage polarities are reversed from the polarities shown.

[0062]FIG. 7c is a cross-sectional drawing illustrating an alternateaspect of the circular waveguide slot antenna of FIG. 7a with multiplefixed dielectric constant layers. The dielectric with the fixeddielectric forms a first layer 710 a underlying the dielectric with thefixed dielectric constant 712, and a second layer 710 b overlies thedielectric with the ferroelectric material 712. The two fixed dielectriclayers need not necessarily have the same dielectric constant orthickness. Further, three or more fixed dielectric layers may be used.Alternately but not shown, multiple FE layers can be formed around afixed dielectric layer, or multiple layers of both fixed dielectric andFE layers can be used. The multiple FE dielectric layers may havedifferent thickness, be made of different FE materials, or otherwisehave different dielectric constants with respect to the same voltage.

[0063]FIG. 7d is a cross-sectional drawing illustrating an alternateaspect of the circular waveguide slot antenna of FIG. 7a with aninternal layer of FE material. As shown, the dielectric with theferroelectric material 712 is formed internal to the dielectric 710 withthe fixed dielectric constant. Note, multiple internal regions can beformed although only one is shown. Alternately but not shown, thedielectric with the fixed dielectric constant 710 is formed internal tothe FE dielectric 712. It should also be noted that although theinternal region is shown as rectangularly shaped, other shapes such ascircular, cylindrical, and oval shapes are equally practical.

[0064]FIGS. 7e and 7 f are alternate aspects of the circular waveguideslot antenna 700. The slits are not necessary because the radiator 704need not carry a bias voltage. Instead the bias voltage is supplied bypanels 714 and 716. The bias panels 714/716 can be placed in a varietyof positions on either side of the FE dielectric. One panel may even belocated in the slot.

[0065] In some aspects, the dielectric with ferroelectric material 712is formed from barium strontium titanate, Ba_(x)Sr_(1−x)TiO₃ (BSTO).However, alternate FE materials are well known and may performequivalently. Returning the FIG. 7b for example, the dielectric withferroelectric material 712 can be formed in a thin film layer having athickness 714 in the range from 0.15 to 2 microns. Alternately, thedielectric with ferroelectric material 712 is formed in a thick filmhaving a thickness 714 in the range from 1.5 to 1000 microns. In someaspects, the dielectric with ferroelectric material has a dielectricconstant in the range between 100 and 5000 at zero volts. In otheraspects, the dielectric formed from the first material with a fixeddielectric constant and the dielectric formed from the ferroelectricmaterial have a composite dielectric constant in the range between 2 and100 at zero volts.

[0066] The dielectric constant of the FE material can be manipulatedthrough doping and control of the Curie temperature (Tc). Some populardopant materials are tungsten (W), manganese (Mn), and magnesium (Mg),introduced as oxides. However, other equivalent elements in the samecolumn of the periodic table may also be practical. An FE material hasits greatest dielectric constant at Tc, with the dielectric falling offrapidly with changes of temperature in either direction. However, thereis typically less change in dielectric constant for temperature aboveTc. Therefore, the Tc of an FE material is typically chosen to be belowthe operating temperature seen by the dielectric material.

[0067] An antenna built with a dielectric constant of 1 (air) has lessloss than an antenna built with higher dielectric constant material.However, higher dielectric constant materials are often useful inreducing the size (the effective wavelength) of antennas. Generally, anantenna designer seeks a dielectric material with dielectric constant ofless than 100. The FE material dielectric constants can be reduced byadding dopants at the cost of variability (less change in dielectricconstant per bias volt). Suitable tradeoffs between Tc and doping canmake practical a greater than 2:1 change in FE material dielectric forless than a volt change in bias voltage.

[0068]FIG. 8a is a perspective view of the present invention rectangularwaveguide slot antenna 800. The rectangular waveguide antenna isdescribed as comprising a radiator 804 and dielectric 806. However, thedesignations of radiator and counterpoise are arbitrary. As shown, theslot 808 is transverse to the radiator 804, but it need not be. The FEdielectric 806 is located proximate to the slot 808. Away from the slot808, a fixed constant dielectric 807 may be used. In other aspects ofthe rectangular waveguide slot antenna 800, a plurality of slots (notshown) are used.

[0069]FIG. 8b is a cross-sectional drawing illustrating an alternateaspect of the rectangular waveguide slot antenna of FIG. 8a. As shown,the dielectric 806 includes at least one dielectric layer 810 formedfrom a first material with a fixed dielectric constant and a dielectric812 formed from a ferroelectric material with a variable dielectricconstant, adjacent the dielectric 810 with the fixed dielectricconstant. As shown, the dielectric with the FE material 812 overlies thedielectric with the fixed dielectric constant 810. Typically a voltageis applied to a conductor in the vicinity of the FE dielectric layer 812to create a desired dielectric constant. The voltage, represented by the“+” and “−” signs can be supplied. In some aspects, an electricalinsulator (not shown) can be interposed between layer 812 and theconductive radiator 804 to isolate the bias voltage from the ac signalvoltage. However, a sheet of conductor is usually required to evenlydistribute the bias voltage over the FE dielectric 812 that interfereswith the antenna tuning. Therefore, (electrically isolating) slits 809can be formed in the radiator 804 to separate the two bias voltagepolarities. The dc voltages are typically superimposed upon ac signalbeing conducted by the radiator halves. Alternately but not shown, thedielectric formed with the fixed dielectric constant 810 overlies thedielectric with the ferroelectric material 812. Note, in some aspects ofthe antenna the bias voltage polarities are reversed from the polaritiesshown.

[0070]FIG. 8c is a cross-sectional drawing illustrating an alternateaspect of the rectangular waveguide slot antenna of FIG. 8a withmultiple fixed dielectric constant layers. The dielectric with the fixeddielectric forms a first layer 810 a underlying the dielectric with thefixed dielectric constant 812, and a second layer 810 b overlies thedielectric with the ferroelectric material 812. The two fixed dielectriclayers need not necessarily have the same dielectric constant orthickness. Further, three or more fixed dielectric layers may be used.Alternately but not shown, multiple FE layers can be formed around afixed dielectric layer, or multiple layers of both fixed dielectric andFE layers can be used. The multiple FE dielectric layers may havedifferent thickness, be made of different FE materials, or otherwisehave different dielectric constants with respect to the same voltage.

[0071]FIG. 8d is a cross-sectional drawing illustrating an alternateaspect of the rectangular waveguide slot antenna of FIG. 8a with aninternal layer of FE material. As shown, the dielectric with theferroelectric material 812 is formed internal to the dielectric 810 withthe fixed dielectric constant. Note, multiple internal regions can beformed although only one is shown. Alternately but not shown, thedielectric with the fixed dielectric constant 810 is formed internal tothe FE dielectric 812. It should also be noted that although theinternal region is shown as rectangularly shaped, other shapes such ascircular, cylindrical, and oval shapes are equally practical. In anothervariation not shown, equivalent to FIGS. 7e and 7 f, the dc bias voltageis supplied by panels interior to the radiator 804, so that the slits809 need not be formed.

[0072] In some aspects, the dielectric with ferroelectric material 812is formed from barium strontium titanate, Ba_(x)Sr_(1−x)TiO₃ (BSTO).However, alternate FE materials are well known and may performequivalently. Returning the FIG. 8b for example, the dielectric withferroelectric material 812 can be formed in a thin film layer having athickness 814 in the range from 0.15 to 2 microns. Alternately, thedielectric with ferroelectric material 812 is formed in a thick filmhaving a thickness 814 in the range from 1.5 to 1000 microns. In someaspects, the dielectric with ferroelectric material has a dielectricconstant in the range between 100 and 5000 at zero volts. In otheraspects, the dielectric formed from the first material with a fixeddielectric constant and the dielectric formed from the ferroelectricmaterial have a composite dielectric constant in the range between 2 and100 at zero volts.

[0073] The dielectric constant of the FE material can be manipulatedthrough doping and control of the Curie temperature (Tc). Some populardopant materials are tungsten (W), manganese (Mn), and magnesium (Mg),introduced as oxides. However, other equivalent elements in the samecolumn of the periodic table may also be practical. An FE material hasits greatest dielectric constant at Tc, with the dielectric falling offrapidly with changes of temperature in either direction. However, thereis typically less change in dielectric constant for temperature aboveTc. Therefore, the Tc of an FE material is typically chosen to be belowthe operating temperature seen by the dielectric material.

[0074] An antenna built with a dielectric constant of 1 (air) has lessloss than an antenna built with higher dielectric constant material.However, higher dielectric constant materials are often useful inreducing the size (the effective wavelength) of antennas. Generally, anantenna designer seeks a dielectric material with dielectric constant ofless than 100. The FE material dielectric constants can be reduced byadding dopants at the cost of variability (less change in dielectricconstant per bias volt). Suitable tradeoffs between Tc and doping canmake practical a greater than 2:1 change in FE material dielectric forless than a volt change in bias voltage.

[0075]FIGS. 9a and 9 b are partial cross-sectional and plan views,respectively, of the present invention flare-notch antenna. Theflare-notch antenna 900 comprises a counterpoise 902, a radiator 904,and a dielectric 906 a and 906 a, at least one of which including FEmaterial. The designation of counterpoise and radiator may be consideredarbitrary. A slot or notch 907 is shown. The FE dielectric 906 a and 906b are proximately located to the notch 907. Also shown is a feed with acenter conductor 908 and a ground 909.

[0076]FIG. 9c is an alternate aspect of the flare-notch antenna of FIG.9b. As shown, the dielectric 906 a and 906 b includes at least onedielectric layer 910 formed from a first material with a fixeddielectric constant and a dielectric 912 formed from a ferroelectricmaterial with a variable dielectric constant, adjacent the dielectric910 with the fixed dielectric constant. As shown, the dielectric withthe FE material 912 overlies the dielectric with the fixed dielectricconstant 910. Typically a voltage is applied to a conductor in thevicinity of the FE dielectric layer 912 to create a desired dielectricconstant. The voltage, represented by the “+” and “−” signs can besupplied. In some aspects, an electrical insulator (not shown) can beinterposed between layer 912 and the radiator/counterpoise 904/902 toisolate the bias voltage from the ac signal voltage. However, a sheet ofconductor is usually required to evenly distribute the bias voltage overthe FE dielectric 912 that interferes with the antenna tuning.Therefore, the dc voltage is typically superimposed upon ac signal beingconducted by the radiator/counterpoise 904/902, and the reference groundis supplied to conductive panels 914. Alternately but not shown, thedielectric formed with the fixed dielectric constant 910 overlies thedielectric with the ferroelectric material 912. Note, in some aspects ofthe antenna the bias voltage polarities are reversed from the polarityshown.

[0077]FIG. 9d is a plan view illustrating an alternate aspect of theflare-notch antenna of FIG. 9b with multiple fixed dielectric constantlayers. The dielectric with the fixed dielectric forms a first layer 910a underlying the dielectric with the fixed dielectric constant 912, anda second layer 910 b overlies the dielectric with the ferroelectricmaterial 912. The two fixed dielectric layers need not necessarily havethe same dielectric constant or thickness. Further, three or more fixeddielectric layers may be used. Alternately but not shown, multiple FElayers can be formed around a fixed dielectric layer, or multiple layersof both fixed dielectric and FE layers can be used. The multiple FEdielectric layers may have different thickness, be made of different FEmaterials, or otherwise have different dielectric constants with respectto the same voltage.

[0078]FIG. 9e is a plan view illustrating an alternate aspect of theflare-notch antenna of FIG. 9b with an internal layer of FE material. Asshown, the dielectric with the ferroelectric material 912 is formedinternal to the dielectric 910 with the fixed dielectric constant. Note,multiple internal regions can be formed although only one is shown.Alternately but not shown, the dielectric with the fixed dielectricconstant 910 is formed internal to the FE dielectric 912. It should alsobe noted that although the internal region is shown as rectangularlyshaped, other shapes such as circular, cylindrical, and oval shapes areequally practical. In another variation not shown, the FE material formsinternal regions on only one side of the radiator, for example isdielectric 906 a.

[0079] In some aspects, the dielectric with ferroelectric material 912is formed from barium strontium titanate, Ba_(x)Sr_(1−x)TiO₃ (BSTO).However, alternate FE materials are well known and may performequivalently. Returning the FIG. 9c for example, the dielectric withferroelectric material 912 can be formed in a thin film layer having athickness 914 in the range from 0.15 to 2 microns. Alternately, thedielectric with ferroelectric material 912 is formed in a thick filmhaving a thickness 914 in the range from 1.5 to 1000 microns. In someaspects, the dielectric with ferroelectric material has a dielectricconstant in the range between 100 and 5000 at zero volts. In otheraspects, the dielectric formed from the first material with a fixeddielectric constant and the dielectric formed from the ferroelectricmaterial have a composite dielectric constant in the range between 2 and100 at zero volts.

[0080] The dielectric constant of the FE material can be manipulatedthrough doping and control of the Curie temperature (Tc). Some populardopant materials are tungsten (W), manganese (Mn), and magnesium (Mg),introduced as oxides. However, other equivalent elements in the samecolumn of the periodic table may also be practical. An FE material hasits greatest dielectric constant at Tc, with the dielectric falling offrapidly with changes of temperature in either direction. However, thereis typically less change in dielectric constant for temperature aboveTc. Therefore, the Tc of an FE material is typically chosen to be belowthe operating temperature seen by the dielectric material.

[0081] An antenna built with a dielectric constant of 1 (air) has lessloss than an antenna built with higher dielectric constant material.However, higher dielectric constant materials are often useful inreducing the size (the effective wavelength) of antennas. Generally, anantenna designer seeks a dielectric material with dielectric constant ofless than 100. The FE material dielectric constants can be reduced byadding dopants at the cost of variability (less change in dielectricconstant per bias volt). Suitable tradeoffs between Tc and doping canmake practical a greater than 2:1 change in FE material dielectric forless than a volt change in bias voltage.

[0082]FIGS. 10a though 10 d are illustrations of the present inventionopen-ended waveguide antenna 1000. FIG. 10a is a partial cross-sectionalview of the present invention open-ended waveguide antenna with aselectable operating frequency. The open-ended waveguide antenna 1000comprises a radiator 1002 and a dielectric 1006 with ferroelectricmaterial proximately located to the radiator 1002. The dielectric 1006has a varying dielectric constant responsive to a voltage applied to theferroelectric material. The designations of counterpoise and radiatorare arbitrary. Typically, the open ends 1007 are grounded. Away from theopen ends 107 a constant dielectric material 1005 can be used. Theprinciples and design of open-ended antennas are well understood bythose skilled in the art and are not repeated here in the interest ofbrevity. Although the use of FE material gives an open-ended antenna awider range of selectable operating frequencies, the general principlesof design are not changed by the present invention FE material.

[0083] The antenna 1000 has a predetermined fixed characteristicimpedance independent of the resonant frequency. Alternately stated, theantenna 1000 has a predetermined approximately constant gain independentof the resonant frequency.

[0084]FIG. 10b is a cross-sectional drawing illustrating an alternateaspect of the open-ended waveguide antenna of FIG. 10a. As shown, thedielectric 1006 includes at least one dielectric layer 1010 formed froma first material with a fixed dielectric constant and a dielectric 1012formed from a ferroelectric material with a variable dielectricconstant, adjacent the dielectric 1010 with the fixed dielectricconstant. As shown, the dielectric with the FE material 1012 overliesthe dielectric with the fixed dielectric constant 1010. Typically avoltage is applied to a conductor in the vicinity of the FE dielectriclayer 1012 to create a desired dielectric constant. The voltage,represented by the “+” and “−” signs can be supplied. In some aspects,an electrical insulator (not shown) can be interposed between layer 1012and the radiator 1002 to isolate the bias voltage from the ac signalvoltage. However, a sheet of conductor is usually required to evenlydistribute the bias voltage over the FE dielectric 1012 that interfereswith the antenna tuning. Therefore, electrically isolating slits 1009can be formed in the radiator 1002 to separate the two bias voltagepolarities. The dc voltages are typically superimposed upon ac signalbeing conducted by the radiator halves. Alternately but not shown, thedielectric formed with the fixed dielectric constant 1010 overlies thedielectric with the ferroelectric material 1012. Note, in some aspectsof the antenna the bias voltage polarities are reversed from thepolarity shown.

[0085]FIG. 10c is a cross-sectional drawing illustrating an alternateaspect of the open-ended waveguide antenna of FIG. 10a with multiplefixed dielectric constant layers. The dielectric with the fixeddielectric forms a first layer 1010 a underlying the dielectric with thefixed dielectric constant 1012, and a second layer 1010 b overlies thedielectric with the ferroelectric material 1012. The two fixeddielectric layers need not necessarily have the same dielectric constantor thickness. Further, three or more fixed dielectric layers may beused. Alternately but not shown, multiple FE layers can be formed arounda fixed dielectric layer, or multiple layers of both fixed dielectricand FE layers can be used. The multiple FE dielectric layers may havedifferent thickness, be made of different FE materials, or otherwisehave different dielectric constants with respect to the same voltage.

[0086]FIG. 10d is a cross-sectional drawing illustrating an alternateaspect of the open-ended waveguide antenna of FIG. 10a with an internallayer of FE material. As shown, the dielectric with the ferroelectricmaterial 1012 is formed internal to the dielectric 1010 with the fixeddielectric constant. Note, multiple internal regions can be formedalthough only one is shown. Alternately but not shown, the dielectricwith the fixed dielectric constant 1010 is formed internal to the FEdielectric 1012. It should also be noted that although the internalregion is shown as rectangularly shaped, other shapes such as circular,cylindrical, and oval shapes are equally practical. In another variationnot shown, equivalent to FIGS. 7e and 7 f, the dc bias voltage issupplied by panels interior to the radiator 1002, so that the slits 1009need not be formed.

[0087] In some aspects, the dielectric with ferroelectric material 1012is formed from barium strontium titanate, Ba_(x)Sr_(1−x)TiO₃ (BSTO).However, alternate FE materials are well known and may performequivalently. Returning the FIG. 10b for example, the dielectric withferroelectric material 1012 is formed in a thin film layer having athickness 1014 in the range from 0.15 to 2 microns. Alternately, thedielectric with ferroelectric material 1012 is formed in a thick filmhaving a thickness 1014 in the range from 1.5 to 1000 microns. In someaspects, the dielectric with ferroelectric material has a dielectricconstant in the range between 100 and 5000 at zero volts. In otheraspects, the dielectric formed from the first material with a fixeddielectric constant and the dielectric formed from the ferroelectricmaterial have a composite dielectric constant in the range between 2 and100 at zero volts.

[0088] The dielectric constant of the FE material can be manipulatedthrough doping and control of the Curie temperature (Tc). Some populardopant materials are tungsten (W), manganese (Mn), and magnesium (Mg),introduced as oxides. However, other equivalent elements in the samecolumn of the periodic table may also be practical. An FE material hasits greatest dielectric constant at Tc, with the dielectric falling offrapidly with changes of temperature in either direction. However, thereis typically less change in dielectric constant for temperature aboveTc. Therefore, the Tc of an FE material is typically chosen to be belowthe operating temperature seen by the dielectric material.

[0089] An antenna built with a dielectric constant of 1 (air) has lessloss than an antenna built with higher dielectric constant material.However, higher dielectric constant materials are often useful inreducing the size (the effective wavelength) of antennas. Generally, anantenna designer seeks a dielectric material with dielectric constant ofless than 100. The FE material dielectric constants can be reduced byadding dopants at the cost of variability (less change in dielectricconstant per bias volt). Suitable tradeoffs between Tc and doping canmake practical a greater than 2:1 change in FE material dielectric forless than a volt change in bias voltage.

[0090] Returning to FIGS. 10a and 10 b, although an open-endedrectangular waveguide has been depicted, the above analysis anddescription applies to open-ended circular waveguide and open-endedparallel plate antennas. Further, the open-ended waveguide antenna 1000can have a signal feed elected that is a coaxial cable, parallel plates,or any kind of waveguide.

[0091]FIGS. 11a through 11 e are views of the present invention hornantenna with a selectable operating frequency. As seen in FIG. 11a, thehorn antenna 1100 comprises a radiator horn 1102 and a dielectric 1106with ferroelectric material proximately located to the radiator horn.The dielectric 1006 has a varying dielectric constant responsive to avoltage applied to the ferroelectric material. A coaxial feed line 1004with a center conductor 1005 is shown. The horn 1002 has an electricallength 1109 responsive to the dielectric constant. The electrical lengthis constant with respect to the resonant frequency. The horn can beeither grounded or open. Again the designations of counterpoise andradiator are arbitrary. The principles and design of horn antennas arewell understood by those skilled in the art and are not repeated here inthe interest of brevity. Although the use of FE material gives a hornantenna a wider range of selectable operating frequencies, the generalprinciples of design are not changed by the present invention FEmaterial.

[0092] The horn antenna 1100 has a predetermined fixed characteristicimpedance independent of the resonant frequency. Alternately, the hornantenna 1100 has a predetermined approximately constant gain independentof the resonant frequency.

[0093]FIG. 11b is a cross-sectional drawing illustrating an alternateaspect of the horn antenna of FIG. 11a. As shown, the dielectric 1106includes at least one dielectric layer 1110 formed from a first materialwith a fixed dielectric constant and a dielectric 1112 formed from aferroelectric material with a variable dielectric constant, adjacent thedielectric 1110 with the fixed dielectric constant. As shown, thedielectric with the FE material 1112 overlies the dielectric with thefixed dielectric constant 1110. Typically a voltage is applied to aconductor in the vicinity of the FE dielectric layer 1112 to create adesired dielectric constant. The voltage, represented by the “+” and “−”signs can be supplied. In some aspects, an electrical insulator (notshown) can be interposed between layer 1112 and the radiator horn 1102to isolate the bias voltage from the ac signal voltage. However, a sheetof conductor is usually required to evenly distribute the bias voltageover the FE dielectric 1112 that interferes with the antenna tuning.Therefore, electrically isolating slits 1108 can be formed in theradiator 1102 to separate the two bias voltage polarities. The dcvoltages are typically superimposed upon ac signal being conducted bythe radiator halves. Alternately but not shown, the dielectric formedwith the fixed dielectric constant 1110 overlies the dielectric with theferroelectric material 1112. Note, in some aspects of the antenna thebias voltage polarities are reversed from the polarities shown.

[0094]FIG. 11c and 11 d are cross-sectional drawings illustrating analternate aspect of the horn antenna 1100 of FIG. 11a with multiplefixed dielectric constant layers. The dielectric with the fixeddielectric forms a first layer 1110 a underlying the dielectric with thefixed dielectric constant 1112, and a second layer 1110 b overlies thedielectric with the ferroelectric material 1112. The two fixeddielectric layers need not necessarily have the same dielectric constantor thickness. Further, three or more fixed dielectric layers may beused. Alternately but not shown, multiple FE layers can be formed arounda fixed dielectric layer, or multiple layers of both fixed dielectricand FE layers can be used. The multiple FE dielectric layers may havedifferent thickness, be made of different FE materials, or otherwisehave different dielectric constants with respect to the same voltage.

[0095]FIG. 11e is a cross-sectional drawing illustrating an alternateaspect of the horn antenna of FIG. 11a with an internal layer of FEmaterial. As shown, the dielectric with the ferroelectric material 1112is formed internal to the dielectric 1110 with the fixed dielectricconstant. Note, multiple internal regions can be formed although onlyone is shown. Alternately but not shown, the dielectric with the fixeddielectric constant 1110 is formed internal to the FE dielectric 1112.It should also be noted that although the internal region is shown asrectangularly shaped, other shapes such as circular, cylindrical, andoval shapes are equally practical. In another variation not shown,equivalent to FIGS. 7e and 7 f, the dc bias voltage is supplied bypanels interior to the radiator 1002, so that the slits 1108 need not beformed.

[0096] In some aspects, the dielectric with ferroelectric material 1112is formed from barium strontium titanate, Ba_(x)Sr_(1−x)TiO₃ (BSTO).However, alternate FE materials are well known and may performequivalently. Returning the FIG. 11d for example, the dielectric withferroelectric material 1112 can be formed in a thin film layer having athickness 1114 in the range from 0.15 to 2 microns. Alternately, thedielectric with ferroelectric material 1112 is formed in a thick filmhaving a thickness 1114 in the range from 1.5 to 1000 microns. In someaspects, the dielectric with ferroelectric material has a dielectricconstant in the range between 100 and 5000 at zero volts. In otheraspects, the dielectric formed from the first material with a fixeddielectric constant and the dielectric formed from the ferroelectricmaterial have a composite dielectric constant in the range between 2 and100 at zero volts.

[0097] The dielectric constant of the FE material can be manipulatedthrough doping and control of the Curie temperature (Tc). Some populardopant materials are tungsten (W), manganese (Mn), and magnesium (Mg),introduced as oxides. However, other equivalent elements in the samecolumn of the periodic table may also be practical. An FE material hasits greatest dielectric constant at Tc, with the dielectric falling offrapidly with changes of temperature in either direction. However, thereis typically less change in dielectric constant for temperature aboveTc. Therefore, the Tc of an FE material is typically chosen to be belowthe operating temperature seen by the dielectric material.

[0098] An antenna built with a dielectric constant of 1 (air) has lessloss than an antenna built with higher dielectric constant material.However, higher dielectric constant materials are often useful inreducing the size (the effective wavelength) of antennas. Generally, anantenna designer seeks a dielectric material with dielectric constant ofless than 100. The FE material dielectric constants can be reduced byadding dopants at the cost of variability (less change in dielectricconstant per bias volt). Suitable tradeoffs between Tc and doping canmake practical a greater than 2:1 change in FE material dielectric forless than a volt change in bias voltage.

[0099] Returning to FIGS. 11a, the above discussion of horn antennasapplies equally to rectangular waveguide, circular waveguide, andparallel plate horn antennas using a signal feed from a coaxial cable,circular waveguide, rectangular waveguide, or a parallel plate signalfeed.

[0100]FIGS. 12a through 12 f are depictions of the present inventionmonopole antenna with a selectable operating frequency. In FIG. 12a, themonopole antenna 1200 comprises a radiator 1202, a counterpoise 1204,and a dielectric 1206 at least partially surrounding the radiator 1202.The dielectric includes ferroelectric material having a varyingdielectric constant responsive to a voltage applied to the ferroelectricmaterial. The radiator 1202 has an electrical length 1208 responsive tothe dielectric constant. Alternately but not shown, the radiator 1202can be formed in a helical shape. The principles and design of monopoleantennas are well understood by those skilled in the art and are notrepeated here in the interest of brevity. Although the use of FEmaterial gives a monopole antenna a wider range of selectable operatingfrequencies, the general principles of design are not changed by thepresent invention FE material.

[0101] The antenna 1200 has a predetermined fixed characteristicimpedance independent of the resonant frequency. That is, the electricallength of the radiator is constant with respect to the resonantfrequency. Alternately, the antenna 1200 has a predeterminedapproximately constant gain independent of the resonant frequency.

[0102]FIG. 12b is a drawing illustrating an alternate aspect of themonopole antenna of FIG. 12a. As shown, the dielectric 1206 includes atleast one dielectric layer 1210 formed from a first material with afixed dielectric constant and a dielectric 1212 formed from aferroelectric material with a variable dielectric constant, adjacent thedielectric 1210 with the fixed dielectric constant. As shown, thedielectric with the FE material 1212 overlies the dielectric with thefixed dielectric constant 1210. Typically a voltage is applied to aconductor in the vicinity of the FE dielectric layer 1212 to create adesired dielectric constant. The voltage, represented by the “+” and “−”signs can be supplied. In some aspects, an electrical insulator (notshown) can be interposed between layer 1212 and the radiator 1202 toisolate the bias voltage from the ac signal voltage. However, a sheet ofconductor is usually required to evenly distribute the bias voltage overthe FE dielectric 1212 that interferes with the antenna tuning.Therefore, the dc voltage is typically superimposed upon ac signal beingconducted by the radiator 1202, and the reference ground is supplied toconductive panels 1214. Note, in some aspects of the antenna the biasvoltage polarities are reversed. In other aspects, the radiator 1202does not carry a dc bias, the two bias polarities are carried instead bypanels 1214.

[0103]FIG. 12c is a drawing illustrating an alternate aspect of themonopole antenna 1200 of FIG. 12a with multiple fixed dielectricconstant layers. The dielectric with the fixed dielectric forms a firstlayer 1210 a underlying the dielectric with the fixed dielectricconstant 1212, and a second layer 1210 b overlies the dielectric withthe ferroelectric material 1212. The two fixed dielectric layers neednot necessarily have the same dielectric constant or thickness. Further,three or more fixed dielectric layers may be used. Alternately but notshown, multiple FE layers can be formed around a fixed dielectric layer,or multiple layers of both fixed dielectric and FE layers can be used.The multiple FE dielectric layers may have different thickness, be madeof different FE materials, or otherwise have different dielectricconstants with respect to the same voltage.

[0104]FIG. 12d is a drawing illustrating an alternate aspect of themonopole antenna of FIG. 12a with an internal layer of FE material. Asshown, the dielectric with the ferroelectric material 1212 is formedinternal to the dielectric 1210 with the fixed dielectric constant.Note, multiple internal regions can be formed although only one isshown. Alternately but not shown, the dielectric with the fixeddielectric constant 1210 is formed internal to the FE dielectric 1212.It should also be noted that although the internal region is shown asrectangularly shaped, other shapes such as circular, cylindrical, andoval shapes are equally practical.

[0105]FIG. 12e and 12 f illustrate some alternate aspects of the presentinvention monopole antenna.

[0106] In some aspects, the dielectric with ferroelectric material 1212is formed from barium strontium titanate, Ba_(x)Sr_(1−x)TiO₃ (BSTO).However, alternate FE materials are well known and may performequivalently. Returning the FIG. 12b for example, the dielectric withferroelectric material 1212 can be formed in a thin film layer having athickness 1214 in the range from 0.15 to 2 microns. Alternately, thedielectric with ferroelectric material 1212 is formed in a thick filmhaving a thickness 1214 in the range from 1.5 to 1000 microns. In someaspects, the dielectric with ferroelectric material has a dielectricconstant in the range between 100 and 5000 at zero volts. In otheraspects, the dielectric formed from the first material with a fixeddielectric constant and the dielectric formed from the ferroelectricmaterial have a composite dielectric constant in the range between 2 and100 at zero volts.

[0107] The dielectric constant of the FE material can be manipulatedthrough doping and control of the Curie temperature (Tc). Some populardopant materials are tungsten (W), manganese (Mn), and magnesium (Mg),introduced as oxides. However, other equivalent elements in the samecolumn of the periodic table may also be practical. An FE material hasits greatest dielectric constant at Tc, with the dielectric falling offrapidly with changes of temperature in either direction. However, thereis typically less change in dielectric constant for temperature aboveTc. Therefore, the Tc of an FE material is typically chosen to be belowthe operating temperature seen by the dielectric material.

[0108] An antenna built with a dielectric constant of 1 (air) has lessloss than an antenna built with higher dielectric constant material.However, higher dielectric constant materials are often useful inreducing the size (the effective wavelength) of antennas. Generally, anantenna designer seeks a dielectric material with dielectric constant ofless than 100. The FE material dielectric constants can be reduced byadding dopants at the cost of variability (less change in dielectricconstant per bias volt). Suitable tradeoffs between Tc and doping canmake practical a greater than 2:1 change in FE material dielectric forless than a volt change in bias voltage.

[0109]FIGS. 13a through 13 f are drawings of the present inventiondipole antenna with a selectable operating frequency. In FIG. 13a, thedipole antenna 1300 comprises a radiator 1302, a counterpoise 1304, anda dielectric 1306 at least partially surrounding the radiator 1302. Thedielectric 1306 includes ferroelectric material having a varyingdielectric constant responsive to a voltage applied to the ferroelectricmaterial. The radiator and counterpoise have electrical lengths 1308that are responsive to the varying dielectric constant. Alternately butnot shown, the radiator 1302, the counterpoise 1304, or both can beformed in a helical shape. The principles and design of dipole antennasare well understood by those skilled in the art and are not repeatedhere in the interest of brevity. Although the use of FE material gives adipole antenna a wider range of selectable operating frequencies, thegeneral principles of design are not changed by the present invention FEmaterial.

[0110] The antenna 1300 has a predetermined fixed characteristicimpedance independent of the resonant frequency. That is, the radiatorand counterpoise electrical lengths remain constant with respect toresonant frequency. Typically, the electrical length of the radiator1302 and counterpoise 1304 are either one-half or one-quarter thewavelength of the resonant frequency with respect to the dielectric.Alternately, the antenna has a predetermined approximately constant gainindependent of the resonant frequency.

[0111]FIG. 13b is a drawing illustrating an alternate aspect of themonopole antenna of FIG. 13a. As shown, the dielectric 1306 includes atleast one dielectric layer 1310 formed from a first material with afixed dielectric constant and a dielectric 1312 formed from aferroelectric material with a variable dielectric constant, adjacent thedielectric 1310 with the fixed dielectric constant. As shown, thedielectric with the FE material 1312 overlies the dielectric with thefixed dielectric constant 1310. Typically a voltage is applied to aconductor in the vicinity of the FE dielectric layer 1312 to create adesired dielectric constant. The voltage, represented by the “+” and “−”signs can be supplied. In some aspects, an electrical insulator (notshown) can be interposed between layer 1312 and the radiator 1302 toisolate the bias voltage from the ac signal voltage. However, a sheet ofconductor is usually required to evenly distribute the bias voltage overthe FE dielectric 1312 that interferes with the antenna tuning.Therefore, the dc voltage is typically superimposed upon ac signal beingconducted by the radiator 1302, and the reference ground is supplied toconductive panels 1314. Note, in some aspects of the antenna the biasvoltage polarities are reversed. In other aspects, the radiator 1302does not carry a dc bias, the two bias polarities are carried instead bypanels 1314.

[0112]FIG. 13c is a drawing illustrating an alternate aspect of themonopole antenna 1300 of FIG. 13a with multiple fixed dielectricconstant layers. The dielectric with the fixed dielectric forms a firstlayer 1310 a underlying the dielectric with the fixed dielectricconstant 1312, and a second layer 1310 b overlies the dielectric withthe ferroelectric material 1312. The two fixed dielectric layers neednot necessarily have the same dielectric constant or thickness. Further,three or more fixed dielectric layers may be used. Alternately but notshown, multiple FE layers can be formed around a fixed dielectric layer,or multiple layers of both fixed dielectric and FE layers can be used.The multiple FE dielectric layers may have different thickness, be madeof different FE materials, or otherwise have different dielectricconstants with respect to the same voltage.

[0113]FIG. 13d is a drawing illustrating an alternate aspect of themonopole antenna of FIG. 13a with an internal layer of FE material. Asshown, the dielectric with the ferroelectric material 1312 is formedinternal to the dielectric 1310 with the fixed dielectric constant.Note, multiple internal regions can be formed although only one isshown. Alternately but not shown, the dielectric with the fixeddielectric constant 1310 is formed internal to the FE dielectric 1312.It should also be noted that although the internal region is shown asrectangularly shaped, other shapes such as circular, cylindrical, andoval shapes are equally practical.

[0114]FIG. 13e and 13 f illustrate some alternate aspects of the presentinvention monopole antenna.

[0115] In some aspects, the dielectric with ferroelectric material 1212is formed from barium strontium titanate, Ba_(x)Sr_(1−x)TiO₃ (BSTO).However, alternate FE materials are well known and may performequivalently. Returning the FIG. 12b for example, the dielectric withferroelectric material 1212 can be formed in a thin film layer having athickness 1214 in the range from 0.15 to 2 microns. Alternately, thedielectric with ferroelectric material 1212 is formed in a thick filmhaving a thickness 1214 in the range from 1.5 to 1000 microns. In someaspects, the dielectric with ferroelectric material has a dielectricconstant in the range between 100 and 5000 at zero volts. In otheraspects, the dielectric formed from the first material with a fixeddielectric constant and the dielectric formed from the ferroelectricmaterial have a composite dielectric constant in the range between 2 and100 at zero volts.

[0116] The dielectric constant of the FE material can be manipulatedthrough doping and control of the Curie temperature (Tc). Some populardopant materials are tungsten (W), manganese (Mn), and magnesium (Mg),introduced as oxides. However, other equivalent elements in the samecolumn of the periodic table may also be practical. An FE material hasits greatest dielectric constant at Tc, with the dielectric falling offrapidly with changes of temperature in either direction. However, thereis typically less change in dielectric constant for temperature aboveTc. Therefore, the Tc of an FE material is typically chosen to be belowthe operating temperature seen by the dielectric material.

[0117] An antenna built with a dielectric constant of 1 (air) has lessloss than an antenna built with higher dielectric constant material.However, higher dielectric constant materials are often useful inreducing the size (the effective wavelength) of antennas. Generally, anantenna designer seeks a dielectric material with dielectric constant ofless than 100. The FE material dielectric constants can be reduced byadding dopants at the cost of variability (less change in dielectricconstant per bias volt). Suitable tradeoffs between Tc and doping canmake practical a greater than 2:1 change in FE material dielectric forless than a volt change in bias voltage.

[0118]FIG. 14 is a flowchart illustrating the present invention methodfor frequency tuning a single-band wireless communications antenna.Although this method is depicted as a sequence of numbered steps forclarity, no order should be inferred from the numbering unlessexplicitly stated. It should be understood that some of these steps maybe skipped, performed in parallel, or performed without the requirementof maintaining a strict order of sequence. The methods start at Step1400. Step 1402 forms a single-radiator. In some aspects, Step 1404forms a counterpoise to the radiator. Step 1406 forms a dielectric withferroelectric material proximate to the radiator. Step 1408 applies avoltage to the ferroelectric material. Step 1410, in response toapplying the voltage, generates a dielectric constant. Step 1412, inresponse to the dielectric constant, communicates electromagnetic fieldsat a resonant frequency.

[0119] In some aspects of the method a further step, Step 1414 variesthe applied voltage. Then, Step 1416 modifies the resonant frequency inresponse to changes in the applied voltage. In some aspects, modifyingthe resonant frequency includes forming an antenna with a variableoperating frequency responsive to the applied voltage.

[0120] Forming an antenna with a variable operating frequency includesforming an antenna with a predetermined fixed characteristic impedance,independent of the resonant frequency. In other aspects, forming anantenna with a variable operating frequency includes forming an antennawith a predetermined approximately constant gain, independent of theresonant frequency.

[0121] In some aspects, forming a dielectric with ferroelectric materialin Step 1406 includes substeps. Step 1406 a forms the dielectric with adielectric material from a first material having a fixed dielectricconstant. Step 1406 b forms the dielectric with the ferroelectricmaterial having a variable dielectric constant. Then, modifying theresonant frequency in response to the varying dielectric constant inStep 1416 includes modifying the resonant frequency in response to thevarying the dielectric constant of the ferroelectric material.

[0122] In other aspects, forming a dielectric with ferroelectricmaterial in Step 1406 includes forming the dielectric with a pluralityof dielectric materials, each from a material having a fixed dielectricconstant. Alternately, Step 1406 can include forming the dielectric witha plurality of ferroelectric materials, each having a variabledielectric constant.

[0123] In one aspect, Step 1406 includes forming the dielectric with thefixed dielectric constant adjacent the dielectric with the ferroelectricmaterials. In one aspect of the method, Step 1406 a includes forming thedielectric with the fixed dielectric constant adjacent the radiator.Alternately, Step 1406 b includes forming the dielectric with theferroelectric material adjacent the radiator.

[0124] In another aspect, forming a dielectric with a fixed dielectricconstant in Step 1406 a includes forming the dielectric from a materialselected from the group including foam, air, FR4, Aluminina, and TMM.Step 1406 b includes forming the dielectric with the ferroelectricmaterial from barium strontium titanate, Ba_(x)Sr_(1−x)TiO₃ (BSTO).

[0125] In some aspects Step 1406 includes forming the dielectric withferroelectric material includes forming the ferroelectric material in athin film having a thickness in the range from 0.15 to 2 microns.Alternately, a thick film having a thickness in the range from 1.5 to1000 microns can be formed. In some aspects Step 1406 includes forming adielectric with a dielectric constant in the range between 100 and 5000at zero volts. In other aspects, forming the dielectric withferroelectric material includes forming a FE dielectric layer (Step 1406b) and a fixed constant dielectric layer (Step 1406 a) with a compositedielectric constant in the range between 2 and 100 at zero volts.

[0126] In some aspects, communicating electromagnetic fields at aresonant frequency in Step 1412 includes communicating at resonantfrequencies such as 824 and 894 MHz and 1850 and 1990 MHz.

[0127] In some aspects, applying a voltage to the ferroelectric materialin Step 1410 includes applying a relative dc voltage in the rangebetween 0 and 3.3 volts.

[0128]FIG. 15 is a flowchart illustrating an alternate aspect of themethod depicted in FIG. 14. The method starts at Step 1500. Step 1502providing a single-radiator proximate to a dielectric with ferroelectricmaterial. Step 1504 applies a voltage to the ferroelectric material.Step 1506, in response to the applying voltage, varies the dielectricconstant of the ferroelectric material. Step 1508, in response tovarying the dielectric constant of the ferroelectric material, modifiesthe resonant frequency of the radiator.

[0129] A family of antennas fabricated with FE dielectric material hasbeen provided. A few antenna styles have been given to explain thefundamental concepts. However, the present invention is not limited tojust these antenna designs. In fact, the present invention FE dielectricmaterial is applicable to any antenna using a dielectric. Likewise, afew examples of FE dielectric placement have been given, but once againthe present invention is not limited to merely these examples. Othervariations and embodiments of the invention will occur to those skilledin the art.

We claim:
 1. A horn antenna with a selectable operating frequency, thehorn antenna comprising: a radiator horn; a dielectric withferroelectric material proximate to the radiator, the dielectric havinga varying dielectric constant responsive to a voltage applied to theferroelectric material; and, wherein the horn has an electrical lengthresponsive to the dielectric constant.
 2. The horn antenna of claim 1wherein the antenna has a predetermined fixed characteristic impedanceindependent of the resonant frequency.
 3. The horn antenna of claim 1wherein the antenna has a predetermined approximately constant gainindependent of the resonant frequency.
 4. The horn antenna of claim 1wherein the electrical length of the horn is constant with respect tothe resonant frequency.
 5. The horn antenna of claim 1 wherein thedielectric includes: at least one dielectric layer formed from a firstmaterial with a fixed dielectric constant; and, a dielectric formed froma ferroelectric material with a variable dielectric constant, adjacentthe dielectric with the fixed dielectric constant.
 6. The horn antennaof claim 5 wherein the dielectric formed from the ferroelectric materialoverlies the dielectric with the fixed dielectric constant.
 7. The hornantenna of claim 5 wherein the dielectric formed with the fixeddielectric constant overlies the dielectric formed from theferroelectric material.
 8. The horn antenna of claim 5 wherein thedielectric with the fixed dielectric constant forms a first layerunderlying the dielectric with the ferroelectric material, and a secondlayer overlying the dielectric with the ferroelectric material.
 9. Thehorn antenna of claim 5 wherein the dielectric with the ferroelectricmaterial is formed internal to the dielectric with the fixed dielectricconstant.
 10. The horn antenna of claim 5 wherein the dielectric withthe ferroelectric material is formed external to the dielectric with thefixed dielectric constant.
 11. The horn antenna of claim 1 wherein thedielectric with ferroelectric material is formed from barium strontiumtitanate, Ba_(x)Sr_(1−x)TiO₃ (BSTO).
 12. The horn antenna of claim 11wherein the BSTO ferroelectric material includes oxide dopants selectedfrom the group including tungsten, manganese, and magnesium.
 13. Thehorn antenna of claim 11 wherein the dielectric with ferroelectricmaterial has a dielectric constant that doubles in response to a changeof less than 1 volt of bias voltage.
 14. The horn antenna of claim 11wherein the dielectric with ferroelectric material has a dielectricconstant in the range between 100 and 5000 at zero volts.
 15. The hornantenna of claim 5 wherein the dielectric formed from the first materialwith a fixed dielectric constant and the dielectric formed from theferroelectric material have a composite dielectric constant in the rangebetween 2 and 100 at zero volts.
 16. The horn antenna of claim 1 whereinthe dielectric with ferroelectric material is formed in a thin filmlayer having a thickness in the range from 0.15 to 2 microns .
 17. Thehorn antenna of claim 1 wherein the dielectric with ferroelectricmaterial is formed in a thick film having a thickness in the range from1.5 to 1000 microns.
 18. The horn antenna of claim 1 further comprising:a signal feed selected from the group including a coaxial cable,circular waveguide, rectangular waveguide, and a parallel plate signalfeed.